1. Field of the Invention
The present invention relates to a system of energy retrieval and, more particularly, to such a system which is adapted to retrieve thermal energy from waste heat generated by an internal combustion engine, such as used in a road vehicle or stationary power generators.
2. Description of the Prior Art
Environmental concerns have led to the development of internal combustion engines which are specifically designed to reduce fuel consumption and emitted pollutants.
For instance, as disclosed in U.S. Pat. No. 3,979,913 issued on Sep. 14, 1976 to Yates, it has been proposed to direct engine coolant through a manifold area of an internal combustion engine to generate steam to drive a turbine. The output power from the turbine is used to supplement the basic power of the engine or, alternatively, to provide power to auxiliary equipment. A solenoid-operated valve is provided upstream of the engine manifold to allow or prevent engine coolant flow thereto depending on the temperature of the engine manifold.
U.S. Pat. No. 4,031,705 issued on Jun. 28, 1977 to Berg discloses an auxiliary power system in which hot engine coolant and hot engine exhaust gas are circulated through heat exchangers to vaporize a working fluid before the same enters a vapor engine for providing extra power to the main internal combustion engine. A pressure relief valve is employed in conjunction with a linear solenoid valve to control the amount of working fluid flowing through the heat exchangers as a function of the temperature of the working fluid and the hot engine coolant.
Although the systems described in the above mentioned patents are effective, their implementation has been essentially hampered by the size of the equipment needed. Accordingly, there is a need for a new thermal energy retrieval system which can be miniaturized to a size which could fit, for instance, in a truck engine environment.
It is therefore an aim of the present invention to provide a relatively compact thermal energy retrieval system adapted to convert recuperated waste heat produced by an internal combustion engine into mechanical or electrical power.
It is also an aim of the present invention to provide such a new thermal energy retrieval system which is adapted to be retrofitted to existing road vehicles.
Therefore, in accordance with the present invention, there is provided a compact thermal energy retrieval system for an internal combustion engine cooled by an engine coolant, comprising a low boiling point working fluid circulated in a closed cycle. The closed cycle includes an evaporator for heating the working fluid from a liquid state to a high pressure vapor by means of heat generated by the internal combustion engine. The cycle further includes a turbine through which the vapor is passed to develop power and a condenser to cool and condense the vapor emanating from the turbine to a condensed fluid before being re-circulated through the evaporator. Control means are provided for controlling the operation of the thermal energy retrieval system. The control means include a unitary control valve directly mounted in a main line of the thermal energy retrieval system to automatically regulate a mass flow rate of circulation of the working fluid through the evaporator in accordance with the calorific energy of the heat used to evaporate the working fluid, whereby the efficiency of the cycle can be optimized and the thermal energy retrieval system reduced in size.
In accordance with a further general aspect of the present invention, there is provided a compact evaporator for heating a working fluid from a liquid state to a high pressure vapor. The evaporator comprises a container, a heat exchanging panel spirally rolled within the container and defining an internal serpentine passage connected in flow communication with an inlet and an outlet for allowing a working fluid to flow through the serpentine passage. Inlet and outlet means are provided for allowing a heat source fluid to flow through the container on an outside surface of the heat exchanging panel to transfer heat to the working fluid via the heat exchanging panel.